1. Field of the Invention
The invention relates to power shovels, and more particularly to power shovels having a dipper moved by a rope or cable.
2. Reference to the Prior Art
A well-known type of power shovel includes a revolvable upper frame mounted on a mobile base such as crawler tracks. A fixed boom extends upwardly and outwardly from the frame. A dipper handle is mounted on the boom for movement about a rack and pinion or crowd drive mechanism for pivotal and translational (non-pivotal) movement relative to the boom. A dipper is fixed to the end of the dipper handle. The outer end of the boom has thereon a sheave, and a hoist cable or rope extends over the sheave from a winch drum on the frame and is fastened to the dipper to support and partially control movement of the dipper.
The angle between the dipper teeth and the handle (known as the "tooth cutting" angle), is maintained by a pitch brace connected between the dipper and the handle. The pitch brace is typically a rigid length of steel connected by a pin at one end to the dipper and at the other end to the handle. Manually changing the pitch brace is expensive and time-consuming.
U.S. Pat. No. 5,251,389, which is assigned to the assignee hereof, discloses a pitch brace that can be adjusted by turning a collar to vary the length of the brace.
U.S. Pat. No. 3,278,057 discloses a hydraulic mechanism for adjusting the angle of the dipper relative to the dipper handle.
U.S. Pat. No. 3,933,260 discloses an arrangement using two hoist ropes for adjusting the angle of the dipper relative to the dipper handle.